The present invention relates to an improved starter for an engine.
FIG. 6 shows a conventional starter which is for starting an engine and includes a speed reduction planet gear mechanism. The armature 100 of the DC motor of the starter comprises an armature core 101, an armature shaft 102, on the halfway portion of which the armature core is provided, and a commutator 103 fitted on the armature shaft 102 at the rear portion of the armature 100 and connected to an armature coil 104 provided on the armature core 101. A holder 105 for brushes located in contact with the commutator 103 is coupled to a rear cover 107 by bolts 106. A bearing 108 for supporting the armature shaft 102 at the rear end thereof is fitted in the recess of the rear cover 107. A plurality of permanent magnets 190a for applying a magnetic field to the armature 100 are secured on the inside circumferential surface of the yoke 109 of the DC motor. A front cover 111 fitted with the internal gear 110 of the speed reduction planet gear mechanism is thereof. A plurality of planet gears 113 are engaged with the internal gear 110 and the spur gear 112. Bearings 114 are fitted in the planet gears 113, and are supported by pins 115 secured to a flange 116 constituting the arm of the speed reduction mechanism. An output rotary shaft 117 is secured to the flange 116. A sleeve bearing 118 is fitted in the boss of the internal gear 110, and supports the output rotary shaft 117. A sleeve bearing 119 is fitted in the recess of the rear portion of the output rotary shaft 117, and supports the armature shaft 102 at the front end thereof. A steel ball 120 is provided between the ends of the armature shaft 102 and the output rotary shaft 117 to transmit a thrust. Helical splines 121 are formed on the outside circumferential surface of the halfway portion of the output rotary shaft 117, and are engaged with those of an overrunning clutch 122 so that the clutch is slidable backward and forward. A stopper 123 is provided on the output rotary shaft 116 at the front end thereof to restrict the quantity of the axial movement of a pinion 124 coupled to the overrunning clutch 122. A sleeve bearing 125 is fitted in the anterior part of the front cover 111, and supports the output rotary shaft 117 at the front end thereof. A lever 126 is provided with a pivot 126a at the plastic halfway portion of the lever, and is fitted to the actuator 128 of an electromagnetic switch 127 and the peripheral portion of the overrunning clutch 122 at the ends of the lever. A movable contact 129 is attached with an electric insulator 130 to a rod 131 fitted in a core 132 so that the rod is slidable backward and forward. A fixed contact 133 is secured by a nut 134 to a cap 135 made of an electric insulator. An electromagnetic coil 136 for moving the actuator 128 is provided on a plastic bobbin 137, and is housed in a case 138. A lead wire 139 connects the fixed contact 133 to one of the brushes. A spring 140 is housed in the actuator 128 to push the overrunning clutch 122 through the action of the lever 126. A spring 141 for returning the actuator 128 is provided further.
The operation of the conventional starter is described in detail hereinbelow. When an ignition switch not shown in FIG. 6 is turned on, the electromagnetic coil 136 of the electromagnetic switch 127 is energized to move the actuator 128 backward to push the rod 131 to put the movable contact 129 into touch with the fixed contact 133. As a result, the armature 100 is energized through the contacts 129 and 133, the lead wire 139, and the brushes so that the armature is rotated. The rotation of the armature 100 is transmitted to the overrunning clutch 122 through the spur gear 112 and the planet gears 113 so that the speed reduction planet gear mechanism makes the rotational speed of the clutch lower than that of the armature. At that time, the pinion 124 engaged with the clutch 122 is rotated. The actuator 128 being moved backward as mentioned above swings the lever 126 counterclockwise (as to FIG. 6) about the pivot 126a to slide the clutch 122 together with the pinion 124 forward in the axial direction thereof to engage the pinion with a ring gear formed on the peripheral portion of a flywheel mounted on the crankshaft of the engine not shown in FIG. 6. The engine thus is started. After that, the overrunning clutch 122 is disengaged from the pinion 124 because of the rotative action of the engine to the pinion, so that the pinion recesses.
Since the axis of the DC motor is parallel with that of the electromagnetic switch 127, it is necessary that the installation space for the switch is provided in a part of the engine or the vehicle. For that reason, the layout of the engine in the vehicle is restricted. This is a problem.
In order to solve the problem, a starter including an electric motor and an electromagnetic switch, which are disposed in series which each other, has been proposed. The basic constitution of the starter is that the armature shaft 202 of the DC motor 201 is hollow, and the actuator rod 204 of the electromagnetic switch 203 is laid in the internal opening 202a of the armature shaft 202 and extends toward an output rotary shaft 205, as shown in FIG. 5. Since the armature shaft 202 of the DC motor 201, the actuator rod 204 of the electromagnetic switch 203, and the output rotary shaft 205 extend along the same axis, the starter is called a coaxial starter. A pinion 206, which is engaged with the ring gear of an engine, is provided at the front end of the output rotary shaft 205 whose rear end is inserted in the internal opening 202a of the armature shaft 202. The output rotary shaft 205 is supported at the inserted portion 205a thereof by a sleeve bearing 207 secured in the internal opening 202a of the armature shaft 202, so that the output rotary shaft is slidable in the axial direction thereof. Driving power is transmitted from the armature shaft 202 of the DC motor 201 to the output rotary shaft 205 by a driving power transmission means 209 including an overrunning clutch 208 which is a one-way clutch. The means 209 also includes a speed reduction planet gear mechanism 210 including a sun gear 210a formed on the outside circumferential surface of the armature shaft 202 at the front end thereof, and planet gears 210b. The overrunning clutch 208 includes an outer member 208a to which support pins 211 for the planet gears 210b are secured, and an inner member 208b engaged with helical splines 205c formed on the outside circumferential surface of the expanded portion 205b of the output rotary shaft 205. However, since a fixed contact 212, a movable contact 213, which is brought into touch with the fixed contact 212 to apply electric power to the DC motor 201, and a cover 214 for the contacts are provided at the rear portion of the electromagnetic switch 203, the total length of the coaxial starter is so large that it interferes with a part of the engine. This is a problem. Since the fixed contact 212 needs to be connected to the brush of the DC motor 201 through a wire 215 outside the body of the starter, the efficiency of assembly of the starter is relatively low. This is another problem. Besides, the wire 215, a screw 216 for attaching the wire, and a screw 217 for attaching a power supply connection terminal are likely to interfere with the engine. This is yet another problem.